[PATCH] mm/mmu_notifier: fix mmu_notifier_range_init warning

[PATCH] mm/mmu_notifier: fix mmu_notifier_range_init warning

[Arnd Bergmann]

The macro version of mmu_notifier_range_init() for CONFIG_MMU_NOTIFIER=n
does not evaluate all its arguments, leading to a warning in one case:

mm/migrate.c: In function 'migrate_vma_pages':
mm/migrate.c:2711:20: error: unused variable 'mm' [-Werror=unused-variable]
  struct mm_struct *mm = vma->vm_mm;

Pass down the 'mm' as into the inline function as well so gcc can
see why the variable exists.

Fixes: 137d92bd73b1 ("mm/mmu_notifier: use structure for invalidate_range_start/end calls v2")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 include/linux/mmu_notifier.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
index 29f7b9670ba3..b13ea00ded5d 100644
--- a/include/linux/mmu_notifier.h
+++ b/include/linux/mmu_notifier.h
@@ -476,6 +476,7 @@ struct mmu_notifier_range {
 };
 
 static inline void _mmu_notifier_range_init(struct mmu_notifier_range *range,
+					    struct mm_struct *mm,
 					    unsigned long start,
 					    unsigned long end)
 {
@@ -484,7 +485,7 @@ static inline void _mmu_notifier_range_init(struct mmu_notifier_range *range,
 }
 
 #define mmu_notifier_range_init(range, mm, start, end, event) \
-	_mmu_notifier_range_init(range, start, end)
+	_mmu_notifier_range_init(range, mm, start, end)
 
 
 static inline int mm_has_notifiers(struct mm_struct *mm)
-- 
2.20.0

Re: [PATCH] mm/mmu_notifier: fix mmu_notifier_range_init warning

[Jerome Glisse]

On Tue, Dec 11, 2018 at 09:04:43PM +0100, Arnd Bergmann wrote:
> The macro version of mmu_notifier_range_init() for CONFIG_MMU_NOTIFIER=n
> does not evaluate all its arguments, leading to a warning in one case:
> 
> mm/migrate.c: In function 'migrate_vma_pages':
> mm/migrate.c:2711:20: error: unused variable 'mm' [-Werror=unused-variable]
>   struct mm_struct *mm = vma->vm_mm;
> 
> Pass down the 'mm' as into the inline function as well so gcc can
> see why the variable exists.
> 
> Fixes: 137d92bd73b1 ("mm/mmu_notifier: use structure for invalidate_range_start/end calls v2")

What about changing migrate.c (i actualy tried to do that everywhere in
the patchset but i missed that spot) So we avoid one useless variable on
such configuration:

diff --git a/mm/migrate.c b/mm/migrate.c
index f02bb4b22c1a..883fce631f47 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2701,7 +2701,6 @@ static void migrate_vma_pages(struct migrate_vma *migrate)
 	const unsigned long npages = migrate->npages;
 	const unsigned long start = migrate->start;
 	struct vm_area_struct *vma = migrate->vma;
-	struct mm_struct *mm = vma->vm_mm;
 	struct mmu_notifier_range range;
 	unsigned long addr, i;
 	bool notified = false;
@@ -2724,8 +2723,8 @@ static void migrate_vma_pages(struct migrate_vma *migrate)
 			if (!notified) {
 				notified = true;
 
-				mmu_notifier_range_init(&range, mm, addr,
-							migrate->end,
+				mmu_notifier_range_init(&range, vma->vm_mm,
+							addr, migrate->end,
 							MMU_NOTIFY_CLEAR);
 				mmu_notifier_invalidate_range_start(&range);
 			}


> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  include/linux/mmu_notifier.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
> index 29f7b9670ba3..b13ea00ded5d 100644
> --- a/include/linux/mmu_notifier.h
> +++ b/include/linux/mmu_notifier.h
> @@ -476,6 +476,7 @@ struct mmu_notifier_range {
>  };
>  
>  static inline void _mmu_notifier_range_init(struct mmu_notifier_range *range,
> +					    struct mm_struct *mm,
>  					    unsigned long start,
>  					    unsigned long end)
>  {
> @@ -484,7 +485,7 @@ static inline void _mmu_notifier_range_init(struct mmu_notifier_range *range,
>  }
>  
>  #define mmu_notifier_range_init(range, mm, start, end, event) \
> -	_mmu_notifier_range_init(range, start, end)
> +	_mmu_notifier_range_init(range, mm, start, end)
>  
>  
>  static inline int mm_has_notifiers(struct mm_struct *mm)
> -- 
> 2.20.0
> 

Re: [PATCH] mm/mmu_notifier: fix mmu_notifier_range_init warning

[David Rientjes]

On Tue, 11 Dec 2018, Jerome Glisse wrote:

> On Tue, Dec 11, 2018 at 09:04:43PM +0100, Arnd Bergmann wrote:
> > The macro version of mmu_notifier_range_init() for CONFIG_MMU_NOTIFIER=n
> > does not evaluate all its arguments, leading to a warning in one case:
> > 
> > mm/migrate.c: In function 'migrate_vma_pages':
> > mm/migrate.c:2711:20: error: unused variable 'mm' [-Werror=unused-variable]
> >   struct mm_struct *mm = vma->vm_mm;
> > 
> > Pass down the 'mm' as into the inline function as well so gcc can
> > see why the variable exists.
> > 
> > Fixes: 137d92bd73b1 ("mm/mmu_notifier: use structure for invalidate_range_start/end calls v2")
> 
> What about changing migrate.c (i actualy tried to do that everywhere in
> the patchset but i missed that spot) So we avoid one useless variable on
> such configuration:
> 
> diff --git a/mm/migrate.c b/mm/migrate.c
> index f02bb4b22c1a..883fce631f47 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -2701,7 +2701,6 @@ static void migrate_vma_pages(struct migrate_vma *migrate)
>  	const unsigned long npages = migrate->npages;
>  	const unsigned long start = migrate->start;
>  	struct vm_area_struct *vma = migrate->vma;
> -	struct mm_struct *mm = vma->vm_mm;
>  	struct mmu_notifier_range range;
>  	unsigned long addr, i;
>  	bool notified = false;
> @@ -2724,8 +2723,8 @@ static void migrate_vma_pages(struct migrate_vma *migrate)
>  			if (!notified) {
>  				notified = true;
>  
> -				mmu_notifier_range_init(&range, mm, addr,
> -							migrate->end,
> +				mmu_notifier_range_init(&range, vma->vm_mm,
> +							addr, migrate->end,
>  							MMU_NOTIFY_CLEAR);
>  				mmu_notifier_invalidate_range_start(&range);
>  			}

Wouldn't it be better to just declare mmu_notifier_range_init() as a 
static inline function rather than a #define to avoid this warning?

Re: [PATCH] mm/mmu_notifier: fix mmu_notifier_range_init warning

[Jerome Glisse]

On Tue, Dec 11, 2018 at 01:12:54PM -0800, David Rientjes wrote:
> On Tue, 11 Dec 2018, Jerome Glisse wrote:
> 
> > On Tue, Dec 11, 2018 at 09:04:43PM +0100, Arnd Bergmann wrote:
> > > The macro version of mmu_notifier_range_init() for CONFIG_MMU_NOTIFIER=n
> > > does not evaluate all its arguments, leading to a warning in one case:
> > > 
> > > mm/migrate.c: In function 'migrate_vma_pages':
> > > mm/migrate.c:2711:20: error: unused variable 'mm' [-Werror=unused-variable]
> > >   struct mm_struct *mm = vma->vm_mm;
> > > 
> > > Pass down the 'mm' as into the inline function as well so gcc can
> > > see why the variable exists.
> > > 
> > > Fixes: 137d92bd73b1 ("mm/mmu_notifier: use structure for invalidate_range_start/end calls v2")
> > 
> > What about changing migrate.c (i actualy tried to do that everywhere in
> > the patchset but i missed that spot) So we avoid one useless variable on
> > such configuration:
> > 
> > diff --git a/mm/migrate.c b/mm/migrate.c
> > index f02bb4b22c1a..883fce631f47 100644
> > --- a/mm/migrate.c
> > +++ b/mm/migrate.c
> > @@ -2701,7 +2701,6 @@ static void migrate_vma_pages(struct migrate_vma *migrate)
> >  	const unsigned long npages = migrate->npages;
> >  	const unsigned long start = migrate->start;
> >  	struct vm_area_struct *vma = migrate->vma;
> > -	struct mm_struct *mm = vma->vm_mm;
> >  	struct mmu_notifier_range range;
> >  	unsigned long addr, i;
> >  	bool notified = false;
> > @@ -2724,8 +2723,8 @@ static void migrate_vma_pages(struct migrate_vma *migrate)
> >  			if (!notified) {
> >  				notified = true;
> >  
> > -				mmu_notifier_range_init(&range, mm, addr,
> > -							migrate->end,
> > +				mmu_notifier_range_init(&range, vma->vm_mm,
> > +							addr, migrate->end,
> >  							MMU_NOTIFY_CLEAR);
> >  				mmu_notifier_invalidate_range_start(&range);
> >  			}
> 
> Wouldn't it be better to just declare mmu_notifier_range_init() as a 
> static inline function rather than a #define to avoid this warning?

The define trick is use to drop the event parameter so that we do not
need to define the event value for CONFIG_MMU_NOTIFIER=n case.

Cheers,
Jérôme

Re: [PATCH] mm/mmu_notifier: fix mmu_notifier_range_init warning

[David Rientjes]

On Tue, 11 Dec 2018, Jerome Glisse wrote:

> > > > The macro version of mmu_notifier_range_init() for CONFIG_MMU_NOTIFIER=n
> > > > does not evaluate all its arguments, leading to a warning in one case:
> > > > 
> > > > mm/migrate.c: In function 'migrate_vma_pages':
> > > > mm/migrate.c:2711:20: error: unused variable 'mm' [-Werror=unused-variable]
> > > >   struct mm_struct *mm = vma->vm_mm;
> > > > 
> > > > Pass down the 'mm' as into the inline function as well so gcc can
> > > > see why the variable exists.
> > > > 
> > > > Fixes: 137d92bd73b1 ("mm/mmu_notifier: use structure for invalidate_range_start/end calls v2")
> > > 
> > > What about changing migrate.c (i actualy tried to do that everywhere in
> > > the patchset but i missed that spot) So we avoid one useless variable on
> > > such configuration:
> > > 
> > > diff --git a/mm/migrate.c b/mm/migrate.c
> > > index f02bb4b22c1a..883fce631f47 100644
> > > --- a/mm/migrate.c
> > > +++ b/mm/migrate.c
> > > @@ -2701,7 +2701,6 @@ static void migrate_vma_pages(struct migrate_vma *migrate)
> > >  	const unsigned long npages = migrate->npages;
> > >  	const unsigned long start = migrate->start;
> > >  	struct vm_area_struct *vma = migrate->vma;
> > > -	struct mm_struct *mm = vma->vm_mm;
> > >  	struct mmu_notifier_range range;
> > >  	unsigned long addr, i;
> > >  	bool notified = false;
> > > @@ -2724,8 +2723,8 @@ static void migrate_vma_pages(struct migrate_vma *migrate)
> > >  			if (!notified) {
> > >  				notified = true;
> > >  
> > > -				mmu_notifier_range_init(&range, mm, addr,
> > > -							migrate->end,
> > > +				mmu_notifier_range_init(&range, vma->vm_mm,
> > > +							addr, migrate->end,
> > >  							MMU_NOTIFY_CLEAR);
> > >  				mmu_notifier_invalidate_range_start(&range);
> > >  			}
> > 
> > Wouldn't it be better to just declare mmu_notifier_range_init() as a 
> > static inline function rather than a #define to avoid this warning?
> 
> The define trick is use to drop the event parameter so that we do not
> need to define the event value for CONFIG_MMU_NOTIFIER=n case.
> 

Hmm, strange that Arnd's build failure is only reporting about an unused 
variable instead of MMU_NOTIFY_CLEAR being undefined :/

I think this should be done so that anybody using 
mmu_notifier_range_init() doesn't need to worry about the implications of 
*any* unused formal parameter as a result of how the #define is formed:

diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
--- a/include/linux/mmu_notifier.h
+++ b/include/linux/mmu_notifier.h
@@ -10,21 +10,6 @@
 struct mmu_notifier;
 struct mmu_notifier_ops;
 
-#ifdef CONFIG_MMU_NOTIFIER
-
-/*
- * The mmu notifier_mm structure is allocated and installed in
- * mm->mmu_notifier_mm inside the mm_take_all_locks() protected
- * critical section and it's released only when mm_count reaches zero
- * in mmdrop().
- */
-struct mmu_notifier_mm {
-	/* all mmu notifiers registerd in this mm are queued in this list */
-	struct hlist_head list;
-	/* to serialize the list modifications and hlist_unhashed */
-	spinlock_t lock;
-};
-
 /**
  * enum mmu_notifier_event - reason for the mmu notifier callback
  * @MMU_NOTIFY_UNMAP: either munmap() that unmap the range or a mremap() that
@@ -53,6 +38,21 @@ enum mmu_notifier_event {
 	MMU_NOTIFY_SOFT_DIRTY,
 };
 
+#ifdef CONFIG_MMU_NOTIFIER
+
+/*
+ * The mmu notifier_mm structure is allocated and installed in
+ * mm->mmu_notifier_mm inside the mm_take_all_locks() protected
+ * critical section and it's released only when mm_count reaches zero
+ * in mmdrop().
+ */
+struct mmu_notifier_mm {
+	/* all mmu notifiers registerd in this mm are queued in this list */
+	struct hlist_head list;
+	/* to serialize the list modifications and hlist_unhashed */
+	spinlock_t lock;
+};
+
 struct mmu_notifier_range {
 	struct mm_struct *mm;
 	unsigned long start;
@@ -483,9 +483,14 @@ static inline void _mmu_notifier_range_init(struct mmu_notifier_range *range,
 	range->end = end;
 }
 
-#define mmu_notifier_range_init(range, mm, start, end, event) \
-	_mmu_notifier_range_init(range, start, end)
-
+static inline void mmu_notifier_range_init(struct mmu_notifier_range *range,
+					   struct mm_struct *mm,
+					   unsigned long start,
+					   unsigned long end,
+					   enum mmu_notifier_event event)
+{
+	_mmu_notifier_range_init(range, start, end);
+}
 
 static inline int mm_has_notifiers(struct mm_struct *mm)
 {

Re: [PATCH] mm/mmu_notifier: fix mmu_notifier_range_init warning

[Arnd Bergmann]

On Tue, Dec 11, 2018 at 10:43 PM David Rientjes <rientjes@google.com> wrote:
>
> On Tue, 11 Dec 2018, Jerome Glisse wrote:

>
> Hmm, strange that Arnd's build failure is only reporting about an unused
> variable instead of MMU_NOTIFY_CLEAR being undefined :/
>
> I think this should be done so that anybody using
> mmu_notifier_range_init() doesn't need to worry about the implications of
> *any* unused formal parameter as a result of how the #define is formed:

Your patch below is more or less what I tried at first, and that resulted
in another build failure for

mm/hugetlb.c:   mmu_notifier_range_init(&range, mm, start, end,
MMU_NOTIFY_CLEAR);
mm/hugetlb.c-   adjust_range_if_pmd_sharing_possible(vma,
&range.start, &range.end);

where range.end refers to a nonexisting member of range.

          Arnd

Re: [PATCH] mm/mmu_notifier: fix mmu_notifier_range_init warning

[Jerome Glisse]

On Tue, Dec 11, 2018 at 10:53:03PM +0100, Arnd Bergmann wrote:
> On Tue, Dec 11, 2018 at 10:43 PM David Rientjes <rientjes@google.com> wrote:
> >
> > On Tue, 11 Dec 2018, Jerome Glisse wrote:
> 
> >
> > Hmm, strange that Arnd's build failure is only reporting about an unused
> > variable instead of MMU_NOTIFY_CLEAR being undefined :/
> >
> > I think this should be done so that anybody using
> > mmu_notifier_range_init() doesn't need to worry about the implications of
> > *any* unused formal parameter as a result of how the #define is formed:
> 
> Your patch below is more or less what I tried at first, and that resulted
> in another build failure for
> 
> mm/hugetlb.c:   mmu_notifier_range_init(&range, mm, start, end,
> MMU_NOTIFY_CLEAR);
> mm/hugetlb.c-   adjust_range_if_pmd_sharing_possible(vma,
> &range.start, &range.end);
> 
> where range.end refers to a nonexisting member of range.
> 
>           Arnd

I will post a v3 with htmldoc fix and build warning fix incorporated.

Cheers,
Jérôme

Re: [PATCH] mm/mmu_notifier: fix mmu_notifier_range_init warning

[David Rientjes]

On Tue, 11 Dec 2018, Arnd Bergmann wrote:

> > Hmm, strange that Arnd's build failure is only reporting about an unused
> > variable instead of MMU_NOTIFY_CLEAR being undefined :/
> >
> > I think this should be done so that anybody using
> > mmu_notifier_range_init() doesn't need to worry about the implications of
> > *any* unused formal parameter as a result of how the #define is formed:
> 
> Your patch below is more or less what I tried at first, and that resulted
> in another build failure for
> 
> mm/hugetlb.c:   mmu_notifier_range_init(&range, mm, start, end,
> MMU_NOTIFY_CLEAR);
> mm/hugetlb.c-   adjust_range_if_pmd_sharing_possible(vma,
> &range.start, &range.end);
> 
> where range.end refers to a nonexisting member of range.
> 

Isn't that separate?  It seems like there is a strict dependency that 
CONFIG_HUGETLBFS has on CONFIG_MMU_NOTIFIER.